Semiconductor devices are made from multi-layer structures that are fabricated on semiconductor wafers. The multi-layer structures can include dielectric materials between metallization interconnect lines. In very large scale integration (VLSI) and ultra large scale integration (ULSI) circuits, metal interconnect lines and vias provide interconnection of integrated circuits in semiconductor devices. In a dual damascene process, a dielectric layer is patterned with openings for conductive lines and vias. The openings are filled with metal and provide interconnects for integrated circuits. The dual damascene process is also used to form multilevel conductive lines of metal in insulating layers of multilayer substrates on which semiconductor devices are mounted.
As the demand for faster device speeds continues to increase, dielectric materials with lower dielectric constants, i.e., “low-k” dielectrics, are being used. The speed of an interconnect structure can be characterized in terms of RC (resistance/capacitance) delays. Low-k materials reduce inter-metal capacitance and therefore can reduce delays and provide for faster devices.